I know someone who rode part of RAGBRAI pregnant but I don't remember how far along she was and it was only one day, not the whole week. It is more than likely going to be incredibly hot and humid that week and Muirenn is right, you'll be surrounded by other cyclists who don't know how to ride in a group. For a lot of people it's the only time they ride their bikes for the year and it's one big party. There are so many accidents that happen that I would be wary of going. Plus this year it's going through Des Moines which makes me think it'll have even more riders than normal. I've only participated in it once and that was enough for me to realize it's not my thing. I grew up in Iowa and enjoy the backroads more on my own than with 10,000 other people.

Not to say you couldn't do some of it. Depends how you feel at the time and it might be worth it to do a day or two, but the whole week might not be reasonable. I don't think I would do it.